Lubricating lacquer component, lubricating lacquer and methods for coating elastomers such as windscreen wiper blades

ABSTRACT

A lubricant varnish component and a lubricant varnish, in particular for coating elastomer profiles, are proposed. The lubricant varnish component contains a polyurethane, a siloxane as well as a polyamide powder, a polyethylene powder or a solution of a polyamide. The lubricant varnish may additionally contain a curing agent, in particular an isocyanate-based curing agent. In addition, a first method for coating elastomers is proposed, the proposed lubricant varnish first being applied in the form of a coating to an elastomer profile, and this coating then being dried and/or thermally crosslinked. Furthermore, an alternative, second method is proposed, the proposed lubricant varnish, having or not having polyamide or polyethylene, first being applied in the form of a first coat to the elastomer profile, and an alcoholic or aqueous solution of a polyamide in the form of a second coat or a polyamide powder or a polyethylene powder then being applied to the first coat. The proposed lubricant varnish is suitable in particular for the production of coated windshield wiper blades having a reduced coefficient of dry friction.

[0001] The present invention relates to a lubricant varnish coatingcomponent, a lubricant varnish prepared therewith and methods forcoating elastomers, in particular elastomer profiles, such as windshieldwiper blades, using this lubricant varnish, according to the genericpart of the independent claims.

BACKGROUND INFORMATION

[0002] In the case of windshield wiper blades, it is important that theyare able to adapt as well as possible to the contour of the windshieldof the motor vehicle and remain flexible even at different temperatures.Wiper blades are, as a rule, therefore produced from elastomer profiles,rubber materials, such as natural rubber or chloroprene rubber,substantially being used. In addition, wiper blades made of siliconerubber or polyurethane rubber are also known.

[0003] Compared to materials such as glass or plastic, elastomers havehigh coefficients of sliding friction so that, in the case of aspecified vertical contact force of an elastomer profile in the form ofa windshield wiper blade on the surface of a glass windshield, amultiple of the contact force frequently has to be applied for ahorizontal movement. If the windshield wiper is operated under wetconditions, this presents no substantial problems since a thinlubricating film between the windshield wiper blade and the windshieldis formed by the water film on the windshield so that hydrodynamiclubrication is established. However, problems occur when the windshieldwiper blade is operated without water as a lubricating film, for examplein summer or after short rain showers. Under such conditions, thewindshield dries quickly, with the result that the coefficient offriction increases sharply, which may lead to squeaking, chattering oreven stoppage of the windshield wiper.

[0004] Chlorination or bromination of the surface of the windshieldwiper blade, i.e. curing, has frequently been carried out to date inorder to reduce the coefficient of friction of windshield wiper bladeson a dry glass windshield. However, this requires very exact processcontrol and is not unproblematic in terms of environmental protection.

[0005] Furthermore, it has already been proposed to provide elastomerprofiles with a coating which in particular reduces the coefficient offriction under dry conditions, i.e. the coefficient of dry frictionμ_(dry). Thus, in JP 55 015 873, a wiper lip is coated with a siliconerubber into which molybdenum disulfide has been introduced as a drylubricant for reducing the coefficient of friction. A similar approachis adopted by DE 38 38 904, in which a polyurethane lacquer is used as abinder, into which graphite powder has been incorporated.

[0006] In addition, DE 38 39 937 A1 discloses a one-componentpolyurethane lacquer which contains reactive polysiloxanes for coatingelastomers. EP 293 084 A1 describes a coating which also contains anadditive, such as carbon black, Teflon, graphite or talc, in addition toa polyurethane and a siloxane. Coatings which have a low coefficient offriction under dry conditions can be produced with this material onelastomers.

SUMMARY OF THE INVENTION

[0007] Compared to the related art, the lubricant varnish componentaccording to the present invention, the lubricant varnish according tothe present invention and the methods, according to the presentinvention, for coating elastomers have the advantage that a coatingwhich has a particularly low coefficient of dry friction can be producedtherewith in particular on windshield wiper blades, so that such wiperblades have particularly advantageous properties on dry or dryingvehicle windshields.

[0008] In particular, the force necessary for moving the wiper arm overthe windshield is substantially reduced by the coating according to thepresent invention, so that the electric motor driving the wiper arm canalso be designed to be smaller. This also permits the use of moreeconomical motors and reduces the energy consumption in the motorvehicle. The advantages are noticeable in particular in vehicle types inwhich large, flat windshields, which require very long wiper arms andwiper blades, are provided for reducing the air resistance.

[0009] It is furthermore advantageous that a reduction of unpleasantnoises, such as squeaking or chattering, is achieved by the coatingaccording to the present invention on windshield wiper blades.

[0010] A further advantage of the lubricant varnish according to thepresent invention and of the methods according to the present inventionis that a coating produced therewith on a windshield wiper blade ensuresconstant good wiping quality over a relatively long period, inparticular corresponding to the time between the normal inspectionintervals of a motor vehicle. In particular, the lubricant varnishaccording to the present invention has very good adhesion to andabrasion resistance on elastomer profiles.

[0011] Compared to the halogenation of elastomer profiles which is knownfrom the related art, the methods according to the present inventionhave the advantage that the applied lubricant varnish can be appliedreliably with constant quality and simple process engineering. Moreover,the lubricant varnish according to the present invention is distinctlymore environmentally friendly.

[0012] Advantageous further developments of the present invention areevident from the measures mentioned in the subclaims.

[0013] Thus, it is advantageous if the lubricant varnish according tothe present invention is present in the form of an aqueous 1-componentor 2-component varnish which constitutes no danger to the environment.In this way, the process costs are reduced and storage is simplified.

[0014] It is furthermore advantageous that the lubricant varnish can beapplied in a variety of ways, for example by spraying, dipping orbrushing.

[0015] In addition, the application of the coating to the elastomers isadvantageously effected even before their vulcanization, so that theenergy supplied during the vulcanization can simultaneously be used forfinal curing and/or thermal crosslinking, and the final curing of thelubricant varnish furthermore takes place in a very short time.Moreover, owing to the higher reactivity of the unvulcanized material,better crosslinking of the coating with the elastomer forming thesubstrate is achieved in this case.

[0016] Alternatively, however, coating may also be applied after thevulcanization. This makes it possible to apply the coating outside theproduction line for the elastomer profiles.

[0017] An isocyanate-based curing agent has proven particularlyadvantageous as a curing agent which may be added to the lubricantvarnish component.

EXEMPLARY EMBODIMENTS

[0018] The present invention relates to a varnish sold by Henkel KGaA,Düsseldorf, under the trade name Sipiol® and intended for coatingelastomers. This Sipiol® varnish, which has a polyurethane system whichcontains reactive polysiloxanes, is especially suitable for coatingrubber profiles. The polysiloxanes crosslink with the polyurethanesystem so that they form a component which reduces the coefficient offriction and is integrated in the polymer. Depending on the choice ofthe specific Sipiol® coating, it is initially present in the form of anaqueous 1-component varnish or 2-component varnish and additionallycontains carbon black as an additive.

[0019] Specifically, customary elastomer profiles for windshield wiperrubbers were initially coated with a Sipiol®-based lubricant varnish ina comparative experiment. For this purpose, the coating componentSipiol® WL 2000-21 sold by Henkel KGaA, which is present in the form ofa carbon black-containing suspension, was mixed in the ratio 100:6 withthe isocyanate-based curing agent WV20, likewise sold by Henkel KGaA, inaccordance with instructions. This lubricant varnish was then applied inthe form of a coat to the elastomer profiles which had been pretreatedbeforehand, to improve the adhesion, with a primer likewise sold byHenkel KGaA under the name Cuvertin® X8536.

[0020] After the application of this lubricant varnish to the elastomerprofile, this was then dried for 90 minutes at 90° C. and cut, and thecoefficient of dry friction against glass was then determined. Thismeasurement gave still relatively high, unsatisfactory coefficients ofdry friction μ_(dry) of from 1.5 to 2.5. Furthermore, the wiper rubberwas greatly stretched in the longitudinal direction to check theadhesive strength of the coating produced. The coating adhered very wellto the elastomer profile, i.e. in particular no detachment was found.

[0021] A second comparative experiment was based on the coating systemSipiol® WL 1000-21, which is likewise sold by Henkel KGaA and islikewise present in the form of a carbon black-containing suspension,with which, however, in contrast to the Sipiol® WL 2000-21 system, nocuring agent need be mixed prior to coating, i.e. it is a 1-componentsystem. Otherwise the procedure was as before. Results obtained with thecuring agent-free system Sipiol® WL 1000-21 were analogous to thoseobtained with the system Sipiol® WL 2000-21 to which curing agent wasadded.

[0022] As a result of the comparative experiments, it may thus be statedthat these known lubricant varnishes do not, to be sure, havesufficiently low coefficients of dry friction but are suitable forproducing a firmly adhering coating on elastomer profiles. One of theselubricant varnishes is therefore used below as a matrix system to whichfurther additives or dry lubricants which result in a substantialreduction in the coefficient of dry friction are added.

[0023] It was found that in particular polyamide powder, polyethylenepowder or a solution of polyamide is suitable as an additive. Lubricantvarnishes modified in this manner lead to very firmly adhering coatingson elastomer profiles, having particularly low coefficients of dryfriction μ_(dry) of less than 1.5, in some cases less than 1.0, which atthe same time are abrasion resistant and resistant to weathering. Inaddition, they exhibit no transfer to the opposite body, i.e. the wipedglass. This is important especially in the case of windshields, forensuring that no undesired greasy film which might impair the vision isleft behind.

[0024] Specifically, in a first exemplary embodiment of the invention,starting from the Sipiol® WL 2000-21 system mentioned, to which theisocyanate-based curing agent WV20 was added as a curing agent, oralternatively starting from the curing agent-free system Sipiol® WL1000-21, 1 g of a polyamide powder having as small a particle size aspossible, preferably less than 10 μm, in particular less than 5 μm, wasadded per 10 ml of curing agent-free or curing agent-containing coatingsystem. The suspension obtained was then thoroughly stirred and was thenapplied in the form of a coating to a still unvulcanized, extrudedelastomer profile, which had been shaped into a windshield wiper blade.The elastomer profile was also pretreated beforehand with the primerCuvertin® X8536, which is a solution of chlorinated polymers in organicsolvents, for improving the adhesion. The application of the coating onthe elastomer profile was effected by dipping in the example described.

[0025] By the way, the Sipiol® systems mentioned are aqueouspolyurethane-polysiloxane dispersions which also contain furtheradditives. Further details on these products known per se from HenkelKGaA can be obtained from the corresponding data sheets.

[0026] After application of the described lubricant varnish containing apolyurethane, a siloxane, optionally the curing agent and the polyamidepowder, introduced as an additive, in the form of a thin coating to theelastomer profile, drying was initially carried out for 10 minutes at120° C. Thereafter, the coated elastomer profile was cut and thecoefficient of dry friction μ_(dry) against glass was measuredanalogously to the comparative experiment. Coefficients of dry frictionwhich were substantially reduced compared to the latter which weremeasured, lying between μ_(dry)=0.9 to 1.5.

[0027] By using particularly fine polyamide powders having particlesizes of, preferably, less than 10 μm, it is achieved that no adverseeffects on the wiping pattern in the case of a wet windshield occur withthe use of the coated elastomer profiles as windshield wiper blades.

[0028] The solids proportion of the added polyamide powder in thelubricant varnish may be up to 90 percent by weight, based on theprepared lubricant varnish suspension. It is preferably less than 25percent by weight, since in some cases the coating obtained does notremain sufficiently resilient at higher proportions, i.e. reducedadhesion of the coating on the elastomer profile occurs.

[0029] As an alternative to the ultrafine polyamide powder added, apolyethylene powder is also suitable as a pulverulent additive for thelubricant varnish component or the lubricant varnish. Polyethylenepowders having an ultrahigh molecular weight have proven particularlyadvantageous, the particle size of the powder particles being likewisesupposed be less than 10 μm.

[0030] In a second exemplary embodiment, 1.5 g of polyethylene powderhaving an ultrahigh molecular weight were added to 10 ml of the mixtureof one of the Sipiol® coating systems, i.e. Sipiol® WL 2000-21containing the curing agent WV20 described or Sipiol® WL 1000-21 withoutcuring agent, according to the first exemplary embodiment. For example,a polyethylene powder sold under the name PE-UHMW Hostalen® GUR 2126 byTicona, Oberhausen, is suitable for this purpose.

[0031] The lubricant varnish obtained after addition of thispolyethylene powder was once again applied, as already described above,to an elastomer profile and was dried for 15 minutes at 120° C. Aftersubsequent cutting, the coefficient of dry friction against glass wasdetermined analogously to the above exemplary embodiment or thecomparative experiment, coefficients of dry friction of about 0.4 to 0.5being measured. To this extent, polyethylene powder is a suitable drylubricant or additive for a lubricant varnish for obtaining coats onwindshield wipers having very low coefficients of dry friction.

[0032] A third exemplary embodiment once again starts from one of theSipiol® coating systems already described and according to the first orsecond exemplary embodiment. Furthermore, an alcoholic or aqueoussolution of a polyamide is added to this coating, the polyamidecontained therein acting as an additive which reduces the dry frictionrelative to glass and, as a result of the addition in dissolved form,has a very fine distribution in the base system or matrix system havingpolyurethane and siloxane. In particular, this achieves that sufficientpolyamide is available as a dry lubricant everywhere in the coating.

[0033] Soluble polyamides which may be used are, for example, allpolyamides or copolyamides soluble in alcohol. The use of anN-methoxymethylated polyamide has proven particularly advantageous. Inaddition, it is advantageous if a compound catalyzing the crosslinkingof the dissolved additive polyamide is added to the lubricant varnish.In particular, an organic acid is suitable for this purpose. In thisway, two interpenetrating, insoluble networks form with the crosslinkedpolyamide and the crosslinked polyurethane system, it also beingpossible for crosslinking of the polyamide with the polyurethane systemto occur. The mixture of Sipiol® coating system and curing agent orcuring agent-free Sipiol® coating system has the object of ensuring theelastic properties of the coating obtained, while the polyamidecomponent reduces the coefficient of dry friction.

[0034] In this context, it may furthermore be emphasized that it is alsopossible initially to coat the elastomer profile with the unmodifiedSipiol® coating system/curing agent mixture or the curing agent-freeSipiol® coating system, i.e. without the polyamide additive, and then toapply a further, second coat containing the polyamide dissolved inalcohol to this first coat before subsequent final curing. Theapplication of the second coat can be effected both on the alreadyair-dried first coat or wet-in-wet, i.e. on the still wet first coat.This procedure having two coats applied in succession has the advantagethat the first coat imparts in particular improved adhesion on theelastomer profile, while the second coat primarily reduces the dryfriction of the elastomer profile or of the windshield wiper bladerelative to glass.

[0035] Altogether, reduced abrasion and an increased service life of thewindshield wiper blade produced are achieved in this manner. Moreover,an adaptation of the additive or generally of the wiping behavior of theelastomer profile to the windshield type to be wiped can be effected bythe application of the second coat on the elastomer profile providedwith the first coat.

[0036] Specifically, in a fourth exemplary embodiment, the Sipiol®curing agent mixture already described or alternatively the curingagent-free Sipiol® system is once again prepared by stirring accordingto instructions and first diluted with 30% of water in order to reducethe thickness of the subsequently obtained coat compared to theexemplary embodiments having a pulverulent additive.

[0037] This lubricant varnish was then applied to a prepared elastomerprofile and dried at 25° C. in air until no moist parts were any longervisible. A 5% to 10% solution of a polyamide in an ethanol-watermixture, for example a solution of the polyamide Ultramid® 1C, which issold by BASF AG, Ludwigshafen, was then applied in the form of a secondcoat to this first coat. Thereafter, the elastomer profile coated inthis manner was dried at from 90° C. to 120° C. for 15 minutes and cut,and the coefficient of dry friction on glass was then determined asabove. Values of from 0.8 to 1.2 were obtained. This coat, too, showedno detachment and very good adhesion after considerable stretching inthe longitudinal direction.

[0038] Further exemplary embodiments which vary the fourth exemplaryembodiment described above envisage adding an alcoholic polyamidesolution to the finally prepared Sipiol® curing agent mixture or thecuring agent-free Sipiol® system. The mixing ratio of Sipiol® curingagent mixture or Sipiol® system to polyamide was varied from 1:1 to 1:5.Firmly adhering, resilient films which, as a rule, have coefficients ofdry friction of less than 1.2 are also obtained as a coat on elastomerprofiles in this manner. Here too, N-methoxymethylated polyamides whichare chemically crosslinkable using suitable catalysts, such as organicacids, are preferably used.

[0039] A last exemplary embodiment finally envisages first applying oneof the Sipiol® base systems without an additive, i.e. without additionalpolyamide powder or of a polyethylene powder or a solution of polyamide,to an elastomer profile in the form of a coating and only thereafterapplying a fine polyamide powder or a fine polyethylene powder, inparticular a fine polyethylene powder having an ultrahigh molecularweight, to the still wet coat. For this purpose, the powder is, forexample, sprinkled or blown onto the still wet coat and the coat withthe powder incorporated by sprinkling on or blowing on is then dried for15 minutes at 120° C. Subsequent measurements of the coefficients of dryfriction of coated windshield wiper blades produced in this manner gavecoefficients of dry friction of from 0.6 to 0.9.

[0040] Regarding the methods for applying the coatings described to theelastomer profiles and the method for their preparation or their thermalaftertreatment, it may in general also be stated that the elastomerprofiles are produced, as a rule, with the aid of an extruder, thecoatings according to the exemplary embodiments described being appliedthereon preferably immediately after the extrusion, by spraying, dippingor brushing. After the application of the coating, a customaryvulcanization process of the elastomer profile is then carried out, forexample in a salt bath or in an oven, before the coated and vulcanizedelastomer profile is finally cut.

[0041] Alternatively, the application of the coating to the elastomerprofile can, however, also be effected only after vulcanization, which,however, requires a further thermal treatment at, preferably, a lowertemperature than in the case of the preceding vulcanization. Thisthermal treatment is then effected, for example, downstream of the saltbath or downstream of the oven in a further hot zone.

[0042] The thermal treatment during the vulcanization or in thedownstream hot zone effects chemical crosslinking within the coating andalso bonding or crosslinking of the coating with the elastomer profilepresent underneath.

What is claimed is:
 1. A lubricant varnish component, in particular forthe preparation of a lubricant varnish for coating elastomer profiles,having a polyurethane, siloxane and an additive, wherein the additive isa polyamide powder, a polyethylene powder or a solution of a polyamide.2. The lubricant varnish component as recited in claim 1, wherein thepolyamide powder or the polyethylene powder has a particle size of lessthan 10/m.
 3. The lubricant varnish component as recited in claim 1,wherein the solution of the polyamide is an alcoholic or aqueoussolution, in particular an alcoholic solution of an N-methoxymethylatedpolyamide or copolyamide.
 4. The lubricant varnish component as recitedin one of the preceding claims, wherein it is present in the form of anaqueous solution or dispersion.
 5. A lubricant varnish having or beingmade of a lubricant varnish component as recited in one of the precedingclaims.
 6. The lubricant varnish as recited in claim 5, a curing agent,in particular an isocyanate-based curing agent, being added as a furthercomponent to the lubricant varnish.
 7. The lubricant varnish as recitedin claim 5 or 6, wherein a catalyst which catalyzes final curing of thesolution of the polyamide in the lubricant varnish is added.
 8. Thelubricant varnish as recited in one of claims 5 through 7, wherein thesolids proportion of the polyamide and/or of the polyethylene in thelubricant varnish is from 0.5% by weight to 90% by weight.
 9. A methodfor coating elastomers, in particular windshield wiper blades, alubricant varnish as recited in one of claims 5 through 8 being appliedin the form of a coating to an elastomer profile, and the coating thenbeing dried and/or thermally crosslinked.
 10. The method as recited inclaim 9, wherein the coating is applied by spraying, dipping orbrushing.
 11. The method as recited in claim 9 or 10, wherein thecoating is applied to the elastomer profile immediately after itsextrusion and the elastomer profile is vulcanized after the coating; orthe coating is applied to a vulcanized elastomer profile.
 12. A methodfor coating elastomers, in particular windshield wiper blades, alubricant varnish having or not having the additive as recited in one ofclaims 5 through 8 first being applied in the form of a first coat to anelastomer profile; and an alcoholic or aqueous solution of a polyamidein the form of a second coat or a polyamide powder or a polyethylenepowder then being applied to the first coat.
 13. The method as recitedin claim 12, wherein the polyamide powder or the polyethylene powder issprinkled or blown onto the first coat.
 14. The method as recited inclaim 12 or 13, wherein the first coat is first dried before applicationof the second coat or of the powder; or the second coat or the powder isapplied to the still undried first coat.
 15. The method as recited inone of claims 12 through 14, wherein, after application of the secondcoat or of the powder, the coated elastomer profile is subjected to adrying thermal treatment and/or a thermal treatment which thermallycrosslinks at least the first coat.
 16. A method as recited in any ofclaims 12 through 15, wherein the first and/or the second coat isapplied by spraying, dipping or brushing.
 17. The method as recited inone of claims 12 through 16, wherein the first coat is applied to theelastomer profile immediately after its extrusion; and the elastomerprofile provided with the first and second coat or the first coat andthe powder is then vulcanized; or the first and the second coat or thefirst coat and the powder are applied to an already vulcanized elastomerprofile.
 18. The use of a lubricant varnish or of a method as recited inone of the preceding claims for the production of coated windshieldwiper blades having a reduced coefficient of dry friction.